In a process for fabricating a semiconductor device, a semiconductor wafer is thermally treated. For example, in diffusion process, an electrode formed on a compound semiconductor wafer is sintered.
A conventional sinter furnace includes a heating chamber, in which a semiconductor wafer is heated, and a cooling chamber, in which the semiconductor wafer is cooled down. In such a conventional sinter furnace, a semiconductor wafer is conveyed by a delivery arm, between a loader cassette and the heating chamber; between the heating chamber and the cooling chamber; and between the cooling chamber and an un-loader cassette.
Semiconductor wafers contained in the loader cassette are controlled in temperature at about 20° C. The heating chamber includes a hot plate controlled in temperature at 450° C. The cooling chamber includes a cooling plate controlled in temperature at 20° C.
According to the conventional apparatus, a semiconductor wafer of the room temperature is rapidly heated up when the wafer is put onto the heating plate in the heating chamber. The temperature of the semiconductor wafer changes too rapidly, and therefore, the semiconductor wafer may be broken by heat-shock phenomenon. In addition, a semiconductor wafer, which has been heated in the heating chamber, is rapidly cooled down when the wafer is taken out from the heating chamber. That is because the delivery arm is at the room temperature of about 20° C., which is 430° C. different from the semiconductor wafer, which has been already heated. As a result, the semiconductor wafer may be broken by cool-shock phenomenon. Once a semiconductor wafer is broken, semiconductor devices formed thereon can not be used anymore. The above-described problems are remarkable and more serious to compound type of semiconductor wafers, such as GaAs wafers,